Dell Force10 S55T S55 Configuration Guide FTOS 8.3.5.3 - Page 517

Extended Power-via-MDI TLV The PD sends three pieces of information in the LLDP-MED Extended Power-via-MDI TLV: 1. Power Requirement: FTOS honors this and uses it for power allocation. 2. Power Priority-Critical, High, or Low: FTOS honors this information and uses it for power priority calculation. 3. External Power Source: FTOS does not use this information. Determine the Affect of a Port on the Power Budget The PoE power budget is affected differently depending on how PoE is enabled and whether a device is connected: 1. When you configure a port with power inline auto without the max_milliwatts power limit option, power is only allocated after you connect a device to the port. • When you connect a device, the maximum power for the device class is allocated if there is sufficient power in the budget. See Table 27-1 on page 511. • If there is not enough power in the budget, the configuration is maintained and the port waits for power to become available. • If the device advertises its power requirement through LLDP-MED, then FTOS allocates the required amount and returns the remaining amount to the budget. Note: LLDP-MED TLVs are only honored if the port is configured with power inline auto (with or without the max_milliwatts option). 2. When you configure a port with power inline auto with the power limit option max_milliwatts, power is only allocated after you connect a device to the port. • If the maximum power for the device class is less than the power limit you specified, FTOS allocates the required amount and returns the remaining amount to the budget. • If there is not enough power in the budget, the configuration is maintained and the port waits for power to become available. • If the maximum power for the device class is more than than the power limit you specified, FTOS does not allocate any power. Note: When a port is configured with power inline auto (with or without the max_milliwatts option) and the PoE device is disconnected, the allocated power is returned to the power budget. 3. When you configure a port with power inline static without the power limit option (max_milliwatts), FTOS allocates 15.4W (subject to availability and priority) to the port whether or not a device is connected. 4. When you configure a port with power inline static with the power limit option (max_milliwatts), FTOS allocates the specified number of Watts. Power over Ethernet | 517